Separation method of mixed sulfate in serpentine tailing leachate

Abstract

The invention belongs to the technical field of asbestos tailing utilization, and particularly discloses a separation method of mixed sulfate in serpentine tailing leachate. The separation method provided by the invention comprises the following steps: carrying out quantitative analysis on the serpentine leachate, and adjusting the mass ratio of nickel, iron and magnesium elements in the leachate to a set ratio; carrying out spray drying to obtain mixed sulfate dry powder, placing the mixed sulfate dry powder in a fluidized bed for two-stage roasting, and cooling and aging a roasted thermal decomposition product; and carrying out water leaching on the roasting thermal decomposition product by using a multi-stage countercurrent system, and separating to obtain a magnesium sulfate solution and a nickel / iron oxide. The high-purity high-value magnesium sulfate and nickel / iron oxide products are prepared from the asbestos tailings which are low in cost and harmful to the environment, and the effects of turning waste into wealth, improving the ecological environment and improving the economic benefits of enterprises are achieved.

Description

Technical Field

[0001] This invention relates to the field of asbestos tailings utilization technology, and in particular to a method for separating mixed sulfates in serpentine tailings leachate. Background Technology

[0002] Asbestos (serpentine), also known as "asbestos fiber," is a general term for some silicate minerals that can split into elastic fibrous strands. Its chemical formula is 3MgO·2SiO2·2H2O. Besides magnesium and silicon, it mainly contains iron and nickel. Due to its large reserves and significant hazards, the transportation and storage of asbestos not only require huge investments and management costs, consume large amounts of energy, and occupy large amounts of land, but also cause serious environmental pollution. Therefore, researching the comprehensive utilization of asbestos tailings can not only turn waste into treasure and improve the natural ecological environment, but also provide new development paths for asbestos mining enterprises.

[0003] Currently, acid leaching or sulfation roasting are the most common methods for treating asbestos tailings. In these methods, acid leaching or water leaching yields a mixed sulfate solution containing magnesium sulfate, ferric sulfate, and nickel sulfate. If conventional pH adjustment is used to achieve metal separation, it is not only inefficient and results in impure products, but it also increases production costs and reduces economic benefits.

[0004] Therefore, the separation of mixed sulfates in asbestos tailings leachate is crucial and is also one of the most critical steps for the subsequent utilization of magnesium in serpentine. It is necessary to develop a new and efficient method for separating mixed sulfates to obtain high-purity products. Summary of the Invention

[0005] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention provides a method for separating mixed sulfates from serpentine tailings leachate. This invention achieves efficient separation of mixed sulfate salts from serpentine tailings leachate, preparing high-purity magnesium sulfate and nickel / iron oxide products, thus realizing the high-value utilization of serpentine tailings.

[0006] This invention provides a method for separating mixed sulfates from serpentine leachate, comprising the following steps:

[0007] S1. Quantitatively analyze nickel, iron and magnesium in serpentine leachate, add sulfate, and adjust the mass ratio of nickel, iron and magnesium in leachate to the set ratio.

[0008] S2. Spray dry the leachate to obtain mixed sulfate dry powder, and place it in a fluidized bed for two-stage calcination; the first stage calcination is carried out at 450~670℃ for 2~5h; the second stage calcination is carried out at 750~870℃ for 1~3h.

[0009] S3. Cool the calcination thermal decomposition products to 250~350℃ and keep them warm for 3~7 hours;

[0010] S4. The calcination thermal decomposition products were subjected to water leaching using a multi-stage countercurrent system to separate magnesium sulfate solution and nickel / iron oxide.

[0011] According to some embodiments of the present invention,

[0012] According to some embodiments of the present invention, the serpentine leachate is obtained by mixing serpentine with concentrated sulfuric acid, calcining at 300-500°C to obtain calcined residue, leaching the calcined residue with water, and filtering to obtain a mixed sulfate solution, which is the serpentine leachate.

[0013] According to some embodiments of the present invention, in step S1, the set ratio is: nickel: iron: magnesium = (0.4~0.6): (4~6): (35~45).

[0014] This invention has discovered that by adjusting the ratio of nickel, iron, and magnesium in a mixed sulfate solution, Ni and Fe can form a uniform spinel phase, and the presence of an appropriate amount of Ni can inhibit the oxidation of Fe and the decomposition of magnesium sulfate; while a larger proportion of magnesium is more conducive to the formation of stable and non-decomposable magnesium sulfate solid; the mixed sulfate solution treated by this process can also form a homogeneous sulfate mixture in subsequent processing, which is beneficial for element separation.

[0015] According to some embodiments of the present invention, in step S2, the spray drying method is as follows: the leachate is atomized by a centrifugal atomizer, and the droplets are dried under the conditions of hot air temperature of 230~350℃ at the inlet of the spray drying tower and hot air temperature of 110~130℃ at the outlet, to obtain a uniform mixed sulfate dry powder.

[0016] This invention uses spray drying to obtain mixed sulfate powder, whose physicochemical properties are more conducive to subsequent decomposition reactions.

[0017] According to some embodiments of the present invention, in step S2, the first-stage roasting is heated from room temperature to 530-670°C at a heating rate of 8-12°C / min; the second-stage roasting is heated to 780-870°C at a heating rate of 4-6°C / min.

[0018] This invention employs a dynamic two-stage calcination method in a fluidized bed, ensuring uniform heating of the material, sufficient gas-solid contact, more complete decomposition, and preventing agglomeration. It also shapes the precursor into particles or spheres of a specific size to optimize heat conduction and the escape paths of decomposition gaseous products. The rapid heating rate in the first stage of calcination helps avoid Fe... 2+The oxidation process and the heating rate of the second-stage roasting were also explored and optimized to avoid local overheating and partial decomposition of MgSO4 due to excessively rapid heating, as well as low efficiency due to excessively slow heating.

[0019] According to some embodiments of the present invention, in step S2, the atmosphere of the first stage of roasting is an inert gas containing 1% to 3% hydrogen; the atmosphere of the second stage of roasting is an inert gas.

[0020] An inert atmosphere containing hydrogen can prevent Fe 2+ Oxidized to Fe 3+ This avoids interference with separation due to the lower decomposition temperature of the generated Fe2(SO4)3, and also promotes the formation of a specific spinel phase of Ni / Fe that is easier to separate from MgSO4.

[0021] According to some embodiments of the present invention, in step S3, the calcination thermal decomposition product is cooled to 250-350°C at a cooling rate of 8-12°C / min.

[0022] This invention also optimizes the cooling process of the thermal decomposition products after roasting. After roasting, the material is in a high-temperature state. If rapidly cooled (quenched), the extreme temperature difference between the surface and interior of the material will generate enormous thermal stress, potentially leading to microcracks. However, this is an uncontrollable and destructive cracking process. More importantly, trace amounts of low-eutectic phases (such as eutectic formed by impurities and magnesium sulfate) that may exist in the material at high temperatures will rapidly solidify, "welding" the pores and causing the particle surface to become dense or form a glassy hard shell. Controlled-rate cooling allows for slow and uniform shrinkage of the material, providing sufficient time for atoms / ions to arrange themselves in an orderly manner, maintaining and "solidifying" the porous structure formed at high temperatures that facilitates leaching. These open pores are key channels for the subsequent leaching agent (water) to enter the particle interior and for the dissolution and diffusion of magnesium sulfate. Furthermore, slow cooling also stabilizes and crystallizes the impurity phases, reducing their surface activity and gelation tendency, making them more likely to remain as inert solid particles during leaching, thus maintaining the unobstructed pore channels.

[0023] By aging the thermal decomposition products at 250-350℃ for 3-7 hours, the phase can be stabilized, grain boundaries purified, and the surface passivated through low-temperature solid-state reaction and surface reconstruction. Although this temperature is much lower than the sintering temperature, atoms still have a certain diffusion capacity (especially surface and grain boundary diffusion); trace amounts of non-uniform components (such as unreacted trace precursors and dopant ions) can slowly diffuse at this temperature, achieving composition homogenization at the microscale; this ensures that the trace amounts of incompletely decomposed nickel / iron sulfate remaining after pyrolysis are completely converted into oxides, and makes the distribution of iron ions in the crystal lattice more uniform.

[0024] According to some embodiments of the present invention, in step S4, the temperature of the water immersion is 25~80°C.

[0025] According to some preferred embodiments of the present invention, in step S4, the temperature of the water immersion is 50~80°C.

[0026] The beneficial effects of this invention are:

[0027] This invention utilizes low-cost, environmentally hazardous asbestos tailings to produce magnesium sulfate and nickel / iron oxide products, achieving the effect of turning waste into treasure, improving the ecological environment, and increasing the economic benefits of enterprises.

[0028] This invention improves the separation efficiency of magnesium in asbestos tailings by making technical improvements from multiple angles in the separation process of mixed sulfate solution in asbestos tailings leachate, thus achieving efficient utilization of resources; and significantly improves the purity of magnesium sulfate and nickel / iron oxide products, thus realizing high-value utilization of asbestos tailings.

[0029] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Detailed Implementation

[0030] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0031] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0032] Example 1

[0033] This embodiment provides a method for roasting serpentine tailings with concentrated sulfuric acid and separating mixed sulfates from the serpentine tailings leachate. The specific steps are as follows:

[0034] 1) After crushing the serpentine tailings, mix them with concentrated sulfuric acid (98wt%) at a mass ratio of 1:1, heat to 400℃, and roast for 2 hours to obtain roasted residue. Leach the roasted residue with water at a liquid-to-solid ratio of 3:1 at room temperature for 2 hours, and filter to obtain a mixed sulfate solution. (Specific method: transfer the roasted residue to a leaching tank, add room temperature water at a liquid-to-solid mass ratio of 3:1, and mechanically stir at 200-300 rpm for 2 hours at room temperature to fully dissolve soluble magnesium sulfate, ferric sulfate, nickel sulfate, etc. Then, transport the slurry to a plate and frame filter press for solid-liquid separation, using double-layer filter cloth and applying 0.4-0.6...) The pressure is MPa. After the filtrate is collected through filter cloth and filter plate, a clear mixed sulfate solution is obtained. The filter cake is washed once with a small amount of water (about 10% of the mass of the roasted residue). The washing liquid is added to the main filtrate. The final combined liquid is a mixed sulfate solution containing metal ions such as magnesium, iron, and nickel. The content of nickel, iron, and magnesium in the mixed sulfate solution is detected by ICP method. The mass ratio of nickel, iron, and magnesium in the solution is adjusted to 0.5:5:40 by adding their respective sulfates, so that a homogeneous sulfate mixture can be formed in subsequent steps.

[0035] In this embodiment, the mass ratio of nickel, iron, and magnesium in the serpentine tailings is 0.2:4:30.

[0036] 2) The mixed sulfate solution is atomized by a centrifugal atomizer at a speed of 20,000 rpm using a spray drying method. The droplets are rapidly dried under the conditions of 300℃ hot air at the inlet and 120℃ at the outlet of the spray drying tower to obtain a uniform mixed sulfate powder, which provides an ideal homogeneous precursor for subsequent stepwise thermal decomposition.

[0037] 3) Place the mixed sulfate dry powder in a fluidized bed for calcination. First stage calcination: In an argon atmosphere containing 2% (V / V) hydrogen, heat to 550℃ at a heating rate of 10℃ / min and hold for 3h. Second stage calcination: Replace with an argon atmosphere and continue heating to 800℃ at a heating rate of 5℃ / min and hold for 2h.

[0038] 4) Cool the calcined thermal decomposition products at a controlled rate of 10℃ / min to 300℃, and keep them at that temperature for 5 hours to stabilize the Ni / Fe oxide phase and reduce its trace dissolution in subsequent water immersion.

[0039] 5) The thermal decomposition products (including MgSO4, NiO, and Fe2O3) are leached using a three-stage countercurrent leaching system to finally obtain magnesium sulfate solution and nickel / iron oxides;

[0040] The leaching water temperature is 70℃; the specific process of the countercurrent leaching system is as follows:

[0041] ① Solid flow direction (1→2→3):

[0042] Level 1: The newly added solid raw material (from the pyrolysis process of step 4) enters the No. 1 leaching tank and comes into contact with the leachate (called "intermediate liquid") from Level 2, which has already been leached once and has a medium concentration. Since the intermediate liquid is not yet saturated, it will continue to dissolve the remaining MgSO4 in the solid, thus increasing the solution concentration.

[0043] Stage 2: The partially leachable solids separated from stage 1 (containing even less MgSO4) are transported to stage 2 leach tank to come into contact with the lower concentration leachate from stage 3 to further dissolve the remaining MgSO4.

[0044] Stage 3: The almost saturated solids (containing very little MgSO4) separated from tank 2 are transported to leaching tank 3 and come into contact with fresh water (or the lowest concentration of wash water) for final "sweeping" leaching to wash off the last remaining soluble MgSO4; thereafter, the solid residue is filtered and separated and discharged from the system as tailings to obtain nickel / iron oxides.

[0045] ② Liquid flow direction (3→2→1):

[0046] Level 3: Fresh water is added to tank No. 3 and comes into contact with the solid containing the least amount of MgSO4, thus becoming a leachate with a lower concentration.

[0047] Level 2: The lower concentration leachate from tank 3 is pumped into tank 2, and after contacting with solids containing a moderate amount of MgSO4, the concentration increases to a moderate level.

[0048] Stage 1: The medium-concentration leachate from tank 2 is pumped into tank 1 to come into contact with the new solid raw material. Since the MgSO4 content in the solid is the highest at this time, the leaching driving force is the greatest, and the solution concentration is greatly increased to the highest level. The solution flowing out of tank 1 is a high-concentration MgSO4-rich solution, which is then used for subsequent processes (such as evaporation and crystallization) to obtain magnesium sulfate.

[0049] Testing showed that the magnesium separation efficiency in the magnesium sulfate solution obtained in this embodiment was 99.5%, the purity was 99.6%, and the purity of the obtained nickel-iron oxide was 99.3%.

[0050] Example 2

[0051] This embodiment provides a method for roasting serpentine tailings with concentrated sulfuric acid and separating mixed sulfates in the serpentine tailings leachate. This embodiment is basically the same as Embodiment 1, except that the roasting temperature in the first stage of step 3) is adjusted to 650°C.

[0052] Testing showed that the magnesium separation efficiency in the magnesium sulfate solution obtained in this embodiment was 99.6%, the purity was 99.7%, and the purity of the obtained nickel-iron oxide was 99.5%.

[0053] Example 3

[0054] This embodiment provides a method for roasting serpentine tailings with concentrated sulfuric acid and separating mixed sulfates in the serpentine tailings leachate. This embodiment is basically the same as Embodiment 1, except that the roasting temperature in the second stage of step 3) is adjusted to 850°C.

[0055] Testing showed that the magnesium separation efficiency in the magnesium sulfate solution obtained in this embodiment was 99.7%, the purity was 99.8%, and the purity of the obtained nickel-iron oxide was 99.7%.

[0056] Example 4

[0057] This embodiment provides a method for roasting serpentine tailings with concentrated sulfuric acid and separating mixed sulfates in the serpentine tailings leachate. This embodiment is basically the same as Embodiment 1, except that the water leaching temperature in step 5) is adjusted to 50°C.

[0058] Testing showed that the magnesium separation efficiency in the magnesium sulfate solution was 99.3%, the purity was 99.4%, and the purity of the obtained nickel-iron oxide was 99.1%.

[0059] Example 5

[0060] This embodiment provides a method for roasting serpentine tailings with concentrated sulfuric acid and separating mixed sulfates in the serpentine tailings leachate. This embodiment is basically the same as Embodiment 1, except that the water leaching temperature in step 5) is adjusted to room temperature (25°C).

[0061] Testing showed that the magnesium separation efficiency in the magnesium sulfate solution obtained in this embodiment was 95.4%, the purity was 95.7%, and the purity of the obtained nickel-iron oxide was 95.9%.

[0062] Comparative Example 1

[0063] This comparative example provides a method for roasting serpentine tailings with concentrated sulfuric acid and separating mixed sulfates from the serpentine tailings leachate. This comparative example is basically the same as Example 1, except that the roasting temperature in step 3) is adjusted to 300°C.

[0064] The comparative example showed that the magnesium separation efficiency in the magnesium sulfate solution was 80.4%, the purity was 78.6%, and the purity of the obtained nickel-iron oxide was 83.7%.

[0065] Comparative Example 2

[0066] This comparative example provides a method for roasting serpentine tailings with concentrated sulfuric acid and separating mixed sulfates from the serpentine tailings leachate. This comparative example is basically the same as Example 1, except that the roasting temperature in the second stage of step 3) is adjusted to 700°C.

[0067] The comparative example showed that the magnesium separation efficiency in the magnesium sulfate solution was 73.8%, the purity was 75.1%, and the purity of the obtained nickel-iron oxide was 79.7%.

[0068] Comparative Example 3

[0069] This comparative example provides a method for roasting serpentine tailings with concentrated sulfuric acid and separating mixed sulfates in the serpentine tailings leachate. This comparative example is basically the same as Example 1, except that the roasting in step 3) is not a two-stage roasting, but only a second-stage roasting, which is held at 800°C for 3 hours.

[0070] The comparative example showed that the magnesium separation efficiency in the magnesium sulfate solution was 70.8%, the purity was 67.1%, and the purity of the obtained nickel-iron oxide was 73.2%.

[0071] Comparative Example 4

[0072] This comparative example provides a method for separating mixed sulfates from serpentine tailings by roasting them with concentrated sulfuric acid. This comparative example is basically the same as Example 1, except that step 1) is omitted in this comparative example, where additional sulfate is added to adjust the metal element ratio in the mixed sulfate solution.

[0073] The comparative example showed that the magnesium element separation efficiency in the magnesium sulfate solution was 75.7%, the purity was 87.6%, and the purity of the obtained nickel-iron oxide was 80.6%.

[0074] Comparative Example 5

[0075] This comparative example provides a method for roasting serpentine tailings with concentrated sulfuric acid and separating mixed sulfates from the serpentine tailings leachate. This comparative example is basically the same as Example 1, except that in step 2), this comparative example uses a conventional evaporation crystallization method to obtain mixed sulfate solids, which are then made into powder for subsequent roasting steps.

[0076] The comparative example showed that the magnesium separation efficiency in the magnesium sulfate solution was 89.9%, the purity was 89.2%, and the purity of the obtained nickel-iron oxide was 90.6%.

[0077] Comparative Example 6

[0078] This comparative example provides a method for roasting serpentine tailings with concentrated sulfuric acid and separating mixed sulfates from the serpentine tailings leachate. This comparative example is basically the same as Example 1, except that a conventional muffle furnace is used for roasting in step 3) of this comparative example.

[0079] The comparative example showed that the magnesium separation efficiency in the magnesium sulfate solution was 87.3%, the purity was 88.2%, and the purity of the obtained nickel-iron oxide was 89.2%.

[0080] Comparative Example 7

[0081] This comparative example provides a method for roasting serpentine tailings with concentrated sulfuric acid and separating mixed sulfates from the serpentine tailings leachate. This comparative example is basically the same as Example 1, except that the roasting in step 3) of this comparative example is carried out in an air atmosphere.

[0082] The comparative example showed that the magnesium separation efficiency in the magnesium sulfate solution was 92.7%, the purity was 91.6%, and the purity of the obtained nickel-iron oxide was 93.7%.

[0083] Comparative Example 8

[0084] This comparative example provides a method for separating mixed sulfates in the serpentine tailings leachate by using concentrated sulfuric acid mixed with roasted serpentine tailings. This comparative example is basically the same as Example 1, except that in step 5), this comparative example does not use a multi-stage countercurrent leaching method, but instead directly water-leaches the roasted pyrolysis material.

[0085] The comparative example showed that the magnesium separation efficiency in the magnesium sulfate solution was 86.4%, the purity was 87.4%, and the purity of the obtained nickel-iron oxide was 89.7%.

[0086] Comparative Example 9

[0087] This comparative example provides a method for roasting serpentine tailings with concentrated sulfuric acid and separating mixed sulfates from the serpentine tailings leachate. This comparative example is basically the same as Example 1, except that in step 4), the roasted thermal decomposition material is directly cooled to room temperature instead of being aged.

[0088] The comparative example showed that the magnesium separation efficiency in the magnesium sulfate solution was 70.4%, the purity was 73.8%, and the purity of the obtained nickel-iron oxide was 82.7%.

[0089] Analysis of the reasons for the low separation efficiency and product purity in each comparative example:

[0090] Adjusting the roasting process parameters in Comparative Examples 1-3 can lead to incomplete decomposition of nickel sulfate and ferric sulfate in the mixed sulfate, thus affecting the separation of Ni and Fe from magnesium sulfate.

[0091] In Comparative Example 4, the proportion of metal elements in the mixed sulfate was not adjusted, so Ni and Fe could not form a uniform spinel phase. Furthermore, the presence of too little Ni weakened the inhibitory effect on the decomposition of magnesium sulfate, leading to the loss of Mg and a decrease in the purity of the oxide.

[0092] Comparative Example 5 uses evaporation crystallization, which yields blocky or large-particle mixed crystals / crusts. Due to the different solubilities and crystallization rates of nickel sulfate, ferric sulfate, and magnesium sulfate, stepwise crystallization easily occurs, resulting in macroscopic and microscopic inhomogeneity of the product composition (i.e., segregation). Within a large crystal cake, the proportion of metal ions at different locations may vary greatly. Furthermore, the crystallization results in a dense blocky form with poor thermal conductivity, making it difficult for gases generated by internal thermal decomposition to escape, easily leading to incomplete decomposition, bubbling, or bursting, and easily forming a hard shell that hinders further reactions. In addition, evaporation crystallization is usually intermittent and multi-step (evaporation, concentration, crystallization, filtration, drying), which is cumbersome, and the crystallization process itself (crystal nucleation and growth) is difficult to control precisely, resulting in large batch-to-batch variations. In contrast, the solution of this invention uses spray drying to atomize the solution into droplets ranging from several micrometers to tens of micrometers. Each droplet is a "microreactor," and drying is completed in a very short time (within seconds). The resulting spherical powder has a highly uniform composition and the stoichiometry of each particle is basically consistent with that of the original solution. This lays a perfect foundation for the synchronicity of subsequent thermal decomposition reactions. Furthermore, spray drying has a high specific surface area and porous structure, which allows the reaction gases (SO3 / O2, etc.) to diffuse easily during thermal decomposition, resulting in high heat and mass transfer efficiency, more complete and faster decomposition, and less sintering and agglomeration. Moreover, as a continuous, one-step process, its parameters (inlet temperature, atomization rate, feed rate) are easy to precisely control, the product particle size distribution is adjustable, and the reproducibility is good.

[0093] In Comparative Example 6, a conventional muffle furnace was used for calcination. In the muffle furnace, when MgSO4 remains undecomposed while Ni / Fe sulfate decomposes, the resulting NiO / Fe2O3 oxide microcrystals may coat the undecomposed MgSO4 particles, forming a "shell" that severely hinders further decomposition of the internal MgSO4 (if higher temperatures are required) or impedes the dissolution of MgSO4 during water immersion. In contrast, the fluidized bed calcination method used in this example, with its intense scouring and rapid gas removal, effectively prevents the formation and thickening of this coating, solving the "coating" problem. Furthermore, due to the uniform temperature and efficient mass transfer of the fluidized bed calcination method, the reaction can be more precisely controlled at the target temperature, allowing for almost complete decomposition of Ni / Fe sulfate while maximally preserving the MgSO4 from decomposition, thus facilitating subsequent solid-liquid separation during water immersion (MgSO4 decomposes).2+ The process of Ni / Fe entering the solution and remaining in the solid is clearer and more thorough. In addition, the powder produced by fluidized bed calcination has good flowability, uniform particle size, and large specific surface area, which is the ideal feeding state for the subsequent multi-stage countercurrent leaching process in this invention, enabling efficient solid-liquid contact and mass transfer.

[0094] In Comparative Example 7, air calcination was used, Fe 2+ Oxidized to Fe 3+ The decomposition temperature of Fe2(SO4)3 is even lower, which interferes with the separation, making it difficult for Ni / Fe to form a specific spinel state that is easily separated from MgSO4. Therefore, the purity of magnesium sulfate and nickel iron oxide is reduced.

[0095] The example uses heated leaching, which improves leaching kinetics and has a greater thermodynamic tendency to accelerate the dissolution of magnesium sulfate. In contrast, the leaching at room temperature in Comparative Example 8 was not effective.

[0096] Example 5 uses a direct water leaching method, which can also make good use of serpentine, but the magnesium separation efficiency and product purity are reduced. This shows that the multi-stage countercurrent leaching method of the present invention can achieve the maximum enrichment of Mg and improve the leaching rate of Mg.

[0097] In summary, the comparative analysis of the magnesium separation efficiency and product purity of the products obtained from the above embodiments and comparative examples shows that the present invention can achieve efficient separation of metal elements in serpentine tailings, obtain high-value products, and achieve significant economic benefits.

[0098] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for separating mixed sulfates from serpentine leachate, characterized in that, Includes the following steps: S1. Quantitatively analyze nickel, iron and magnesium in serpentine leachate, add sulfate, and adjust the mass ratio of nickel, iron and magnesium in leachate to the set ratio. S2. Spray dry the leachate to obtain mixed sulfate dry powder, and place it in a fluidized bed for two-stage calcination; the first stage calcination is carried out at 450~670℃ for 2~5h; the second stage calcination is carried out at 750~870℃ for 1~3h. S3. Cool the calcination thermal decomposition products to 250~350℃ and keep them warm for 3~7 hours; S4. The calcination thermal decomposition products were subjected to water leaching using a multi-stage countercurrent system to separate magnesium sulfate solution and nickel / iron oxide.

2. The method for separating mixed sulfates from serpentine leachate according to claim 1, characterized in that, The source of the serpentine leachate is as follows: serpentine is mixed with concentrated sulfuric acid and roasted at 300~500℃ to obtain roasted residue. The roasted residue is then soaked in water and filtered to obtain a mixed sulfate solution, which is the serpentine leachate.

3. The method for separating mixed sulfates in serpentine leachate according to claim 1, characterized in that, In step S1, the set ratio is: nickel: iron: magnesium = (0.4~0.6): (4~6): (35~45).

4. The method for separating mixed sulfates from serpentine leachate according to claim 1, characterized in that, In step S2, the spray drying method is as follows: the leachate is atomized by a centrifugal atomizer, and the droplets are dried under the conditions of hot air temperature of 230~350℃ at the inlet of the spray drying tower and hot air temperature of 110~130℃ at the outlet to obtain a uniform mixed sulfate dry powder.

5. The method for separating mixed sulfates from serpentine leachate according to claim 1, characterized in that, In step S2, the first-stage roasting is carried out at a heating rate of 8~12℃ / min from room temperature to 530~670℃; the second-stage roasting is carried out at a heating rate of 4~6℃ / min to 780~870℃.

6. The method for separating mixed sulfates from serpentine leachate according to claim 1, characterized in that, In step S2, the atmosphere of the first stage of roasting is an inert gas containing 1% to 3% hydrogen; the atmosphere of the second stage of roasting is an inert gas.

7. The method for separating mixed sulfates from serpentine leachate according to claim 1, characterized in that, In step S3, the calcination thermal decomposition products are cooled to 250-350℃ at a cooling rate of 8-12℃ / min.

8. The method for separating mixed sulfates from serpentine leachate according to claim 1, characterized in that, In step S4, the temperature of the water immersion is 25~80℃.